I will say that any multiclass system they create should not use XP.
5e is meant to be modular, and XP is a commonly altered or thrown away mechanic.
If you look at 3e, you technically had xp losses for multiclassing outside of favored classes, but I've never used or seen that restriction used in all the 3e games I played....but I'm sure other people did.
So there solution has to be more core to the game, XP won't do the job.
Someone give this man a cigar. I couldnt, apparently I have given you too many.
This is exactly right. For our purposes, we scrapped XP tracking when 3e first came out, and good ridence. If XP tracking is required to enable multiclassing, Im going to cry.
Regardless, I distinctly dislike varying rates of advancement being the balancing/enabling factor for multiclassing just as much as I dislike it for handling class balance (remember the XP charts for the 2e- theif).